Btrfs pool: Replacing 2x500GB mechanical drives with 2x250GB SSD

What's the easiest way to do this?

Want to replace the two 500GB mechanical drives in my cache pool with 2x250GB SSD. There are no other drives in the pool and utilization is about 100GB

Not really sure how integrated the UI is with the btrfs commands (for instance will a device delete command be issued if I remove a drive in the UI and shrink number of disks in pool by 1? Haven't been able to find much info on this here, but perhaps I am looking in the wrong places..

I'm thinking that instead of using UI or by commands going through expanding pool, replacing and rebalancing, it might just be easier to copy all of the pool data on to the array, remove the old pool and create a new one - and then copy pool data back (and re-mark pool based shares as cache-only)

?

Cheers,

T

You have two options, follow the cache replace procedure or let Unraid rebuild mirror, if you opt for the second option:

• Power down server and disconnect one of the cache disks (you can’t just unassign the disk because trying to start array with one unassigned but connected cache disk will make cache appear as unmountable)
   
  
• Start server, assign one of the SSDs as second cache, start array, Unraid will automatically rebuild mirror, you can watch progress on cache web page (balance info)
   
  
• When balance completes repeat process to replace other disk
  

This worked for me but always good to have a cache backup, may also be a good idea to run a scrub before and after.

Thank you for replying.

Looking the procedure you linked to, it seems to apply to single-drive cache scenarios - the article was also last updated (2013) before btrfs pool cache was introduced.

So looks like option 2 is the one that would work for me.

Bonus question: If I wanted to use only one drive for cache, how would I then go about shrinking the pool to only one disk?

Looking the procedure you linked to, it seems to apply to single-drive cache scenarios - the article was also last updated (2013) before btrfs pool cache was introduced.

It should work the same way for a cache pool, after coping data just disconnect old cache disks, connect new ones and create new pool.

Bonus question: If I wanted to use only one drive for cache, how would I then go about shrinking the pool to only one disk?

Shutdown server, disconnect one of the cache disks, start server, start array.

Thanks - I succesfully made the swap today and everything is running fine.

I love this forum